Field of the Invention
The invention relates in general to heat exchangers and in particular to a new and useful cooling device for hot gases in pipes, particularly for hot waste gases from industrial furnaces.
Although the cooling device to which the invention relates can in principle be used in any gas pipe in which hot gases are to be cooled, it will be described hereinafter by reference to the concrete example of its use in industrial furnace waste pipes fitted with a fresh-air intake. Waste gas or gas suction removal pipes of this kind, with a fresh-air intake, whether or not the latter can be regulated, are already known, for example, from electric arc furnaces for the electrical production of steel.
With these furnaces, for reasons explained in detail, for example, in Luxemburg Patent Application No. 80034 of July 24th, 1978, an adjustable intake for additional air or fresh air is preferably provided, downstream of a throttle device, in the gas suction pipe. One purpose of this air intake is to ensure afterburning of the hot waste gases from the furnaces and also to cool the gases.
The cooling of the gases is assisted by a usually water-cooled piece of piping for waste gas, preferably designed on the "pipe-to-pipe" principle, connected up at the point where the intake for additional air is provided in the piping system and hereinafter briefly termed "connection pipe" or "connection piece".
This water-cooled connection pipe, in order to keep the cost moderate and ensure that it does not occupy excessive space, should not be allowed to exceed a certain length, approximately 15 m, but over this length of the connecting pipe, it is desired to cool the gases down by at least 400.degree..
For reasons of energy economy, the proportion of the cooling effect provided by the water-cooled connection pipe by comparison with the part of the cooling action exerted by the additional air should be as great as possible, since not only does the heating undergone by the cooling water represent recoverable energy but a high proportion of fresh air would entail the direct loss of this otherwise recoverable energy, besides which, still more efficient exhauster fans would be required. The practical conclusion to be drawn from these circumstances is that the supply of fresh air should be kept to the indispensable minimum and the hot waste gases brought into as intimate contact as possible with cooling elements which, if necessary, enable energy to be recovered in a usable form. It will be evident from the foregoing that the cooling pipes of the connection pipe constitute cooling elements of this kind.
The fresh air, at a relatively low temperature, is nevertheless fed in at that point on the periphery of the waste gas pipe at which the gases enter the connection pipe. In the latter, therefore, a kind of "funnel" occurs, i.e. a peripheral layer of low temperature fresh air containing a hot "core" of gas. This flow configuration suffers from the dual drawback that the air and gas are only incompletely mixed together, disproportionately large quantities of air therefore being required for the after-burning of the gas, and that the hot gases, contrary to the purpose in view are kept away by the tubular "funnel" of air from the pipe walls to be cooled.
Even if no hose-shaped funnel formed, however, perhaps because suitable measures had been taken to effect the intensive mixing of incoming fresh and of hot gases, it would still not be possible to ensure optimum contact between the entire volume of the mixture on its comparatively short passage through the connection pipe.